Thomas Heatherwick’s magical park will be formed of 300 platforms that resemble toadstools.
Photograph: AP

There’s a combination, it seems, of trees and water and fairytale stories told by a charming inventor, that persuades people to part with many millions – and allows conventional urban planning to be gleefully suspended.

No sooner has the cloud of fairydust surrounding London’s garden bridge proposal begun to settle – after Lambeth council granted half of it planning permission last week (Westminster, across the river, has yet to decide) – than Thomas Heatherwick has sown the seeds for a second magical park to sprout from a river, this time in New York.

It is another vision that could come straight from the set of Avatar – fecund flowerbeds erupting from mushroom-shaped columns, their canopies joining to support parkland above the water. But instead of two toadstools spanning the Thames, there will be a thicket of 300 fungi rising from five to 20 metres above the Hudson River to form an undulating platform of parks and performance spaces.

Just like Heatherwick’s garden bridge proposed for London, this is another vision that could come straight from the set of Avatar. Photograph: AP

Replacing the crumbling ruin of Pier 54, where survivors of the Titanic landed, Heatherwick’s Pier 55 park promises to be a “place of discovery, where visitors can wander and wonder,” with “places to lounge, eat lunch, or just lie in the grass,” building on the appetite for al fresco lazing proven by the success of the nearby High Line park.

There will be a performance space big enough for 1,000 people seated and a further 2,500 sprawled on a lawn, while another 800-seat amphitheatre and a 250-seat stage will nestle in wooded nooks, reached by pathways. It is a Disneyfied confection of woodlands and hills compressed into a miraculous hovering hectare, a place where you might expect the Sylvanian Families to peep out from the undergrowth, or see Florida retirees trundling around in golf carts.

“It’s entirely my fault that this has become so ambitious,” says Barry Diller, the 72-year-old billionaire funder behind the $170m project, former head of Paramount Pictures and Fox, now chairman of internet company IAC. Together with his wife, the fashion designer Diane von Furstenburg, he is committing $130m towards the scheme, while the bulk of the additional $40m will be stumped up by the city and state, topped up by the Hudson River Park Trust.

Pier 55 is set to replace the crumbling ruin of Pier 54, where survivors of the Titanic landed. Photograph: AP

“Frank did these little squiggles and it’s essentially just that,” Diller cheerfully recounts in Sydney Pollack’s Gehry biopic. The bulky pile of white glass is apparently meant to look like the sails of ships coming into harbour, rather than a data centre shed put through the mangle.

For the philanthropic duo – who are also the single largest donors to the High Line – Pier 55 will be the crowning achievement of their ongoing commitment to the city’s Lower West Side, which has transformed from derelict docks, through edgy arts district, to a full-blown open-air mall of luxury boutiques and high-end restaurants over the last 30 years.

“New York has always reminded me of Venice, so I am happy the time has come to properly honour its waterways,” says Von Furstenberg, who is also a major proponent of the $400m Culture Shed project, a visual and performing arts centre to be built in the Hudson Yards development, where the High Line terminates in spectacular fashion to the north.

In the centre of this forthcoming $15bn enclave of towers, Thomas Heatherwick has been summoned once again to conjure what has been hailed as “one of the most expensive works of public art in the world,” a $75m “new icon for the city”. No details have been revealed, but it is thought to have a “gathering” theme. Perhaps petals and stalks and a story of disparate parts coming together will play a part.

For all the ethereal wonder of the Heatherwick touch, and the promise that Pier 55 will be “a new paradigm of public parks,” there are troubling similarities with the garden bridge over the opacity of its origins.

The Pier 55 park is a Disneyfied confection of woodlands and hills compressed into a hovering hectare. Photograph: AP

News of the project might have come as a surprise, because it is: there had been no public mention of the “competition” for the scheme, in which Heatherwick apparently beat off three undisclosed rivals. It is a process echoed across the pond, where Transport for London says it invited a number of unnamed firms to tender for “a living river crossing” between Temple and the south bank, despite the fact that Joanna Lumley and Heatherwick had already launched their garden bridge plan and would be the foregone winners.

It is an alarming situation, in which a private backer leverages substantial public funds for a hazily developed plan, that has not gone unnoticed in either city. £60m has been committed by TfL and the Treasury towards the £175m garden bridge, which is “neither a garden nor a bridge,” in the eyes of the Thames Open Central Space campaign group, who say it will feature less than half a football pitch of green space, “and will bring up to 7 million visitors to a South Bank already bursting with tourists.”

In New York, the Assemblywoman whose district includes the site of the planned park has raised concerns about the secrecy of the Pier 55 process. “It is deeply disturbing that the [Hudson River Park] trust failed until now to disclose what it is doing,” Deborah J Glick, told the New York Times. Others have voiced fears that it represents another example of privately-managed “public” space, while some have questioned whether the city can sustain three more stages, given the competition from other forthcoming cultural venues.

In both rivers, Heatherwick’s magic seeds seem almost certain to sprout, having gained the enthusiastic backing of both mayors, in a serendipitous stroke of Jack and the Beanstalk urban planning. Like the fungi on which they are based, these plans seem to thrive in the dark – but they should not be shielded from the spotlight of public scrutiny any longer.